The subject matter disclosed herein generally relates to a method of creating hardened, erosion resistant stainless steel. More specifically, but not by way of limitation, the present application relates to a method of manufacturing corrosion resistant stainless steel turbine components with regionally increased hardness for improved erosion resistance.
The metal alloys used to make components of gas turbine engines (“gas turbines”), particularly the compressor airfoils of the rotating and stationary blades, must have a combination of high strength, toughness, fatigue resistance, hardness and other physical and mechanical properties in order to provide the operational properties these machines require. Such blades also must have sufficient resistance to various forms of corrosion and corrosion mechanisms, particularly pitting corrosion, due to the extreme operational environments within the turbine, which include exposure to various ionic reactant species, such as chlorides, sulfates, nitrides, etc. Physical erosion is also significant, particularly with gas turbines using “wet compression” processes to increase output. In such cases, water droplets introduced into the intake air may strike and erode the metal along the leading edge of the airfoils, the area of the blade that is most exposed. As will be appreciated, both erosion and corrosion can diminish the other necessary physical and mechanical properties of the blades, such as the high cycle fatigue strength, initiating surface cracks that propagate under the cyclic thermal and mechanical stresses associated with operation of the turbine. Erosion of the leading edge can also lead to increases in operating costs and fuel consumption due to the inefficiencies of the rotors as well as increased carbon emissions.
As disclosed in U.S. patent application Ser. No. 14/632,159, which is hereby incorporated in its entirety in the present application, it will be appreciated that certain stainless steel alloys provide a desirable degree of pitting corrosion resistance. However, as is typical of stainless steel alloys, such performance benefits may be at least partially negated if the hardness of the material is insufficient to adequately slow physical erosion. For example, with regard to compressor airfoils in gas turbines, there is a desire for an increase in the amount of erosion resistance while maintaining the corrosion resistance, so the airfoils can last longer when used for wet compression.
In view of this, a method for producing stainless steel alloys suitable for use in turbine compressor airfoils, with high resistance to both corrosion and erosion degradation would be highly desirable.